Heating and Cooling Equipment

AIR CONDITIONING IS TYPICALLY ASSOCIATED with cooling, but the conditioning of air to provide comfortable conditions for building occupants or processes can apply either to heating or cooling applications. Moisture generation as a by-product of air conditioning is more frequent in cooling due to the condensing of water vapor in the cooling and dehumidification of supply air. In this chapter, references are to cooling rather than heating unless identified as a heating season phenomenon. Space cooling is as a process whereby heat is removed from the space. The heat transfer medium from the space to the air conditioning unit is typically air; space heat is absorbed by the conditioning air. Heat in the air consists of two components: sensible (temperature related) and latent (moisture content). Sensible heat is absorbed through a rise in the supply air temperature. Latent heat is absorbed through a rise in the humidity ratio of the supply air. The conditioning air is then returned to the air conditioning unit, where the absorbed heat is removed at the cooling coil and transferred to a second heat transfer medium (refrigerant) in the cooling coil. Ultimately, in this secondary process, the heat is transferred to the general environment, either to the atmosphere or to water. When considering the impact of air conditioning systems on the formation of mold and mildew, consider how an air conditioning system maintains the humidity of a space within predetermined limits; moisture must be removed at the same rate as it is introduced. If the moisture is thus controlled, little chance will exist for the formation of liquid water through condensation of airborne water vapor. The lack of liquid water within the space will eliminate an essential ingredient for mold and mildew formation.